Influence of jet temperature and nozzle shape on the heat transfer distribution between a smooth plate and impinging air jets

High velocity, impinging, air jets are commonly used for heating, cooling, drying etc., because of the high heat transfer coefficients which occur in the impingement region. To provide data for design, a variety of slot nozzles has been tested to determine the effect on heat transfer of both nozzle shape and slot width. A small heat flux meter was used to measure local values of the heat transfer coefficient in the impingement zone, and these local values were integrated to yield space average values. As a necessary preliminary to the heat transfer investigation, the discharge coefficients of the nozzles were measured. From the first test series it was found that heat transfer results from differently shaped nozzles could be satisfactorily correlated provided that the effective slot width was used to characterize nozzle shape. From the second test series it was found that for geometrically similar arrangements, narrower slots gave higher heat transfer coefficients.

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Twin Pulsating Jets Impingement Heat Transfer for Fuel Preheating in Automotives

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.663.322 ◽

2014 ◽

Vol 663 ◽

pp. 322-328 ◽

Cited By ~ 1

Author(s):

Ali Ahmed Gitan ◽

Rozli Zulkifli ◽

Kamaruzaman Sopian ◽

Shahrir Abdullah

Keyword(s):

Heat Transfer ◽

Ignition Process ◽

Pulsation Frequency ◽

Ir Camera ◽

Copper Target ◽

Air Jets ◽

Air Jet ◽

Impingement Heat Transfer ◽

Pulsating Jet ◽

Pulsating Jets

The problem of environmental pollution and depletion of fossil fuel can be reduced in automotives by using an alternative bio-fuel and improve the ignition process in engine. Both solutions need to use the fuel preheating technique. This work presents the idea of fuel preheating by using exhaust impingement on the fuel tank. Heat transfer between twin pulsating hot air jets and flat copper target was investigated as an application for preheating of automotive fuel to improve ignition process in the engine. The nozzle of 20 mm was used to produce air jet of Reynolds number, Re ≃ 5500 and a temperature of 54°C. The impinged target was imposed to still air surrounding at temperature of 24°C. Pulsating frequencies of 10-50 Hz were applied on air jets by using twin pulsating jet mechanism. The effect of pulsation frequency on heat transfer was measured using IR camera and heat flux-temperature micro foil sensor. The results obtained by both of these methods showed well agreement. Also, the results revealed significant influence of flow rate difference between steady and pulsating jet cases. In addition, the highest Nusselt number, Nu ≃ 7.2, was obtained at pulsation frequency of 20 Hz.

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Time Averaged and Fluctuating Heat Transfer Measurements in an Atomising Mist Jet Nozzle

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11244 ◽

2009 ◽

Author(s):

Oisn F. P. Lyons ◽

Darina B. Murray ◽

Gerard Byrne ◽

Tim Persoons

Keyword(s):

Heat Transfer ◽

Internal Structure ◽

Research Group ◽

Single Phase ◽

Water Mist ◽

Phase Behaviour ◽

Heat Transfer Characteristics ◽

Air Jets ◽

Mist Flow ◽

Jet Nozzle

Much is already known about the heat transfer characteristics of impinging air jets, and they are widely used in many engineering applications. There currently exist many correlations describing such characteristics. However, the complex internal structure of many nozzles can lead these to produce results which deviate from those predicted by correlations. One such nozzle is currently used in this research group to produce a water mist flow and this paper describes the experimental characteristics of its single phase behaviour.

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Experimental Study of Multiple Air Jets Impinging a Moving Flat Plate

Volume 11: Heat Transfer and Thermal Engineering ◽

10.1115/imece2020-23996 ◽

2020 ◽

Author(s):

Flavia Barbosa ◽

Senhorinha Teixeira ◽

Carlos Costa ◽

Filipe Marques ◽

José Carlos Teixeira

Keyword(s):

Heat Transfer ◽

Flat Plate ◽

Jet Impingement ◽

Plate Motion ◽

Test Facility ◽

Flat Plates ◽

Target Plate ◽

Wall Jets ◽

Air Jets ◽

Flow Interactions

Abstract The motion of the target plate is important in some industrial applications which apply multiple jet impingement, such as reflow soldering, drying and food processing. Multiple jet impingement is widely used due to its ability to generate high heat transfer rates over large and complex areas. This convective process is characterized by several flow interactions essentially due to adjacent jets mixing prior the impingement, wall jets collision after the impingement, as well as crossflow interactions induced by the motion of the wall jets that flow through the exits of the domain. These interactions lead to strong flow recirculation, pressure gradients and boundary layer development. However, the complexity of the flow interactions is increased with the surface motion in confined space, due to the generation of strong shear regions. These interactions can induce problems and product defects due to complicated thermal behavior and non-uniform heating or cooling, being important to fully understand the process in order to reduce time and costs. This work addresses the experimental analysis of multiple air jets impinging on a moving flat plate. The experiments are conducted on a purpose-built test facility which has been commissioned, using a 2D-PIV system. Through this technique, the flow structure and velocity profiles will be analyzed in detail. The effects of the impinging plate motion on the resulting global and local velocity profile is compared with a static flat plate. The multiple jet configuration consists on air flowing through 14 circular nozzles, at a Reynolds number of 690 and 1,380. The experiments are conducted for a nozzle-to-plate distance of 8 and a jet-to-jet spacing of 2. The target plate motion remains constant throughout the experiments and equal to 0.03 m/s. The results are compared for both stationary and moving flat plates cases and express the increased complexity of the flow due to strong interaction between jets and the target surface, which affects the heat transfer performance. The results obtained experimentally are important to clearly define this complex flow and these data can be used in future works for numerical model validation.

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The Effect of Entrainment Temperature on Jet Impingement Heat Transfer

Journal of Heat Transfer ◽

10.1115/1.3246655 ◽

1984 ◽

Vol 106 (1) ◽

pp. 27-33 ◽

Cited By ~ 27

Author(s):

S. A. Striegl ◽

T. E. Diller

Keyword(s):

Heat Transfer ◽

Jet Impingement ◽

Local Heat Transfer ◽

Local Heat ◽

Recirculation Region ◽

Measured Temperature ◽

Air Jets ◽

Impingement Heat Transfer ◽

Single Jet ◽

Multiple Plane

An experimental study was done to determine the effect of entrainment temperature on the local heat transfer rates to single and multiple, plane, turbulent impinging air jets. To determine the effect of entrainment of the surrounding fluid, the single jet issued into an environment at a temperature which was varied between the initial temperature of the jet and the temperature of the heated impingement plate. An analytical model was used to correlate the measured heat transfer rate to a single jet. The effect of the entrainment temperature in a single jet was then used to analyze the effect of entrainment from the recirculation region between the jets of a jet array. Using the measured temperature in the recirculation region to include the effect of entrainment, the single jet correlations were successfully applied to multiple jets.

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